This invention relates to an electron feeder for a flat-type luminous device, and more particularly to an electron feeder which is used for a back light device or the like for a flat-type luminous device such as a flat-type display device adapted to display an image or a projected image or display letters, numerals or the like in a predetermined pattern, a non-luminous display device utilizing non-luminous means such as liquid crystal, or the like.
In general, a display device using a cathode ray tube has been conventionally used for displaying an image or a projected image, because a display device of this type carries out a color display with high luminance and high definition. However, a display device of the cathode ray tube type is highly complicated in structure to arrest the weight-saving and thinning of the display device, because it is required to have a considerable depth in order to accomplish the arrangement of an electron gun behind a display plane and the uniform high-voltage scanning of an electron beam between both ends of the display plane.
Also, a display device utilizing an electron excited phosphor is also used for this purpose. This type of display device includes a fluorescent display tube and a fluorescent display device to which the principle of the fluorescent display tube is applied. This fluorescent type of display device includes a thin boxlike envelope evacuated to a high vacuum. On an inner surface of the envelope or in proximity thereto is formed a display section which includes phosphor layers and anode conductors. Also, the device includes a plurality of filamentary cathodes stretchedly arranged opposite to the display section and adapted to emit electrons therefrom when they are electrically heated. Between the filamentary cathodes and the display section or between the filamentary cathodes and the envelope is arranged at least one control electrode, so that the control electrode or the control electrode and anode conductor cause electrons emitted from the filamentary cathodes to be selectively impinged on a desired position on the display section, resulting in a desired display. The application of a low voltage of, for example, several hundred volts or less to the anode conductor or the application of a high voltage of, for example, 5 to 10kV thereto is selectively carried out depending on a display to be desired.
In order to cause the so-constructed fluorescent display device to display an image or a projected image, many filamentary cathodes must be stretchedly arranged so as to prevent nonuniformity in the display and emit electrons sufficient for satisfactory luminescence. This causes an increase in power consumption of the filamentary cathodes and therefore an increase in power consumption of the whole display device. Also, the filamentary cathodes are generally stretched at a position opposite to the display device, therefore, to the filamentary cathodes is adhered a material produced by the decomposition of the phosphor due &o the impingement of electrons on the display section, resulting in the electron discharging capability of the filamentary cathodes being deteriorated. Also, the material causes an oxide formed on the filamentary cathode to be decomposed to produce a decomposition product, so that the product is adhered to an inner surface of the display section which decrease the luminous efficiency of the phosphor, thereby reducing the lifetime of the display device.
Further, in addition to the above-described display device of the cathode ray tube type and the fluorescent display device, a flat-type luminous device using an electron excited phosphor is proposed, which is generally constructed as shown in FIGS. 5(a) and 5(b).
FIG. 5(a) is a side elevation view in section showing such a flat-type luminous device and FIG. 5(b) is a sectional view showing an essential part of the device. The device includes a front cover 1 made of a light-permeable insulating material such as a glass plate or the like. On an inner surface of the front cover 1 are deposited phosphor layers of desired luminous colors and anode conductors of desired patterns, resulting in a display section 2. At a position opposite to the front cover 1 is arranged a rear plate 3 made of an insulating material such as a glass plate. The front cover 1 and rear plate 3 constitute an air-tight envelope in cooperation with side plates 11 by means of a sealing material. On an inner surface of the rear plate 3 is arranged an electron feeder comprising an electron source A and an electron beam guide B in a manner to positionally correspond to the display section 2. Electrons emitted from the electron feeder are selectively impinged on a desired position on the display section 2 by control electrodes 13 or the control electrodes 13 and anode conductors.
Now, the electron source A and electron beam guide B will be described in detail. The electron source A includes a filamentary cathode stretchedly arranged along one side of the flat-type luminous device for emitting electrons therefrom, a reflecting electrode 5 arranged adjacent to the filamentary cathodes 4 for forcing electrons toward the electron stream guide B, a drawing-out electrode 7 positioned opposite to the reflecting electrode 5 with the filamentary cathode 4 being interposed between the the reflecting electrode 5 and the drawing-out electrode 7 and formed at a central portion thereof with a slit-like or ladder-like aperture for drawing out electrons emitted from the cathodes 4 therethrough toward the electron beam guide B, a focusing electrode 6 including one electrode element or a plurality of electrode elements such as a first focusing electrode element 6a, a second focusing electrode element 6b and a third focusing electrode element 6c and adapted to focus electrons drawn out by the drawing-out electrode 7.
The electron beam guide B includes a front electrode 8 arranged in the direction in which the display section 2 extends and is formed with a plurality of apertures 8a and a plurality of rear electrodes 9 arranged along the direction of traveling of the electrons in a manner to be separated from one another.
The front electrode 8 and rear electrodes 9 each have applied thereto a guide voltage higher than a voltage applied to the filamentary cathodes 4 or equal thereto, so that electrons emitted from the electron source A and introduced through one end of the electron beam guide B thereinto may be guided toward the other end of the electron beam guide B. Also, the rear electrodes 9 are selectively applied thereto a voltage lower than the guide voltage constantly applied, to thereby induce the electrons in the direction of the display section 2.
The rear electrodes 9 may comprise a plurality of metal plates. Alternatively, &hey may be formed by depositing a conductive material directly on the rear plate 3.
As described above, the electron feeder for the flat-type luminous device shown in FIGS. 5(a) and 5(b) is so constructed that the electron source is provided with some focusing electrodes for focusing electrons emitted from the filamentary cathodes into a beam-like shape. However, the electron beam guide serves to form a uniform electric field in the guide to reduce an influence on electrons from the electron source by the electric fields of different electrodes, to thereby guide the electrodes in the guide toward the other end of the guide. Accordingly, in the conventional electron feeder, the electron beam guide is not constructed so as to positively focus the electrons.
Thus, the electrons emitted from the electron source are diffused due to a space-charge effect as they travel in the electron beam guide, resulting in flowing into the front electrode and rear electrodes. Accordingly, when the electron feeder is applied to a flat-type luminous device, the electron feeder provides a portion of the display section near the electron source with electrons sufficient for satisfactory luminescence. However, the amount of electrons flowing into the display device is decreased as a distance from the electron source is increased. Thus, the conventional electron feeder has a disadvantage in that the display by the luminous device is increased in luminance near the electron source and gradually darkened with a distance from the electron source, leading to unevenness in the display and non-uniform luminance. Also, electrons in an amount sufficient for the display are produced over only a small distance, resulting in a failure in the largesizing of a display device.
An increase in the number of focusing electrodes for the electron source contributes to the focusing of the electrons emitted from the electron source. However, this also causes an increase in the amount of electrons flowing into the focusing electrodes to decrease electrons flowing into the display section although the electrons are uniformed to some degree, to thereby fail to produce sufficient luminance.